Electrically conductive resinous laminate



P 7, 1954 P. P. RYAN ETAL 2,683,576

ELECTRICALLY CONDUCTIVE RESINOUS LAMINATE Filed Dec. 21, 1949 IN! 'ENTORS PATRICK P E AN Ann I BWLFEEDB-SHEPARDSQN. 1 1 WQ. *M

ATTORNEYS Patented Sept. 7, 1954 ELECTRICALLY CONDUCTIVE RESINOUS LAMI NATE

Patrick P. Ryan and Wilfred B. Shepardson, Trenton, N. J., assignors to St. Regis Paper Company, New York, N. Y., a corporation of New York Application December 21, 1949, Serial No. 134,214

Claims.

This invention pertains to improvements in resinous laminates composed of layers of fibrous sheet material impregnated with and consolidated by a synthetic resin, and pertains more particularly to laminates of this general type but of a novel construction, characterized in being electrically conductive and adapted to electrostatic spray painting or coating. The invention also pertains to novel methods of making the laminates in question and the special resinous varnishes required for producing the same.

Resinous laminates employed in numerous industrial applications require a finishing coat of paint, enamel or the like on one or more surfaces. Examples are breaker strips or door frames for refrigerator cabinets, also inner door panels therefor, automobile trim components, and the like. Since resinous laminates as heretofore produced are substantially non-conductive electrically, being inherently highly insulative electrically; the practice heretofore required for painting or enameling the same has been to apply the coating material by manual brushing or more generally by gun spraying with a spray gun, wherein the brush or spray gun must be directed to all surface portions of the laminate to be coated. This is not only time consuming, but particularly in the case of the spray gun procedure, is extremely wasteful of coating material, since a large proportion thereof is not deposited on the surface to be coated but is wasted in overspray particularly in the case of frame like or open work structures, and also is unevenly coated thereon in excessive amounts over various areas.

These same objections are likewise applicable to the brush or spray gun painting of metal or electrically conductive articles, and to eliminate the same the so-called electrostatic spray painting of metal, and other electrically conductive articles has been developed and widely applied in industry within the past decade or so. According to one modification of this procedure a direct current source or generator of relatively high voltage has its negative terminal connected to the spray gun and its positive terminal connected to the metal or electrically conductive article to be coated. In consequence the particles of coating material being sprayed, become negatively charged and in consequence are attracted and drawn to the article to be coated by reason of its positive polarity. Thus there occurs very little waste of the sprayed coating material since it is attracted to and uniformly deposited on the electrically conductive surface to be coated.

In accordance with another and more preferred procedure for electrostatic spray painting or coating, the electrically conductive articles to be coated are propelled past and in opposed spaced relation to a wire grid or network, between which and a conductive support for the articles, a source of high direct current voltage is applied with its negative pole connected to the wire grid and its positive terminal connected to the conductive article support.

Meantime the coating material is gun sprayed into the space between the wire grid and the articles and in a direction substantially parallel to the direction of article traverse. The resulting spray cloud of coating material assumes a negative charge from the wire grid and is thus attracted to and uniformly deposited on the articles by reason of their positive polarity.

In accordance with the present invention, We have devised resinous laminate constructions of such uniform electrical conductivity throughout, or alternatively over a surface area or areas to be coated, as to be adapted to electrostatic spray coating with substantially the same effectiveness as metal objects. We have also devised novel methods and means for producing such laminates and special resin varnishes required therefor.

In accordance with the basic concept of our invention we produce electrically conductive resinous laminates by impregnating fibrous sheet material, such for example as kraft paper with a thermosetting resin varnish, such as a phenol-, urea-or-melamine-formaldehyde resin varnish, having uniformly dispersed therein, in appropriate concentration and in a suificiently fine state of subdivision, an electrically conductive material such for example as powdered carbon in the form of carbon black or graphite. After oven drying to eliminate volatiles, the so impregnated sheet material may be cut, stacked and hotpressed in a heated press to form a resulting laminate which is electrically conductive throughout and hence adapted to electrostatic spray coating on all surfaces thereof.

Resinous laminates employed as refrigerator or automotive components or the like, such as refrigerator breaker strips or frames, door panels or refrigerator or automotive trim members, ordinarily require painting, enameling, etc. only on one surface or at most on opposite surfaces thereof. We find that for such applications it is not required that the laminate be electrically conductive throughout, it being suflicient that only the surface layer or layers to be coated, be conductive. In accordance with a preferred embodiment of the invention we accordingly form the body portion of the laminate of stacked sheets of fibrous material impregnated with a conventional thermosetting resin varnish such as a phenol-formaldehyde varnish, and superimpose on one or both sides thereof a surface layer or layers of the; fibrous sheet material impregnatect with resin varnish having the finely comminuted conductive material, such as carbon black, dispersed therein. The resulting assembly. is consolidated by hot pressing to producea laminate only one surface layer, or only the opposite surface layers of which, is or are electrically conductive, while the body portionhas the high electrical insulating properties of conventionalelaminates.

We have found that the type, character and amount of the conductive material incorporated in the resin varnish, and the degree of subdivision and dispersion thereof in the varnish. as well as the specific gravity of the resulting varnish, are vital and; controlling factors in the successful production of commercially acceptable electrically conductive resinous laminates in accordance with the invention. Although powdered graphite may be employed exhaustive tests have shown carbon blackto be most suitable, such for example as Cabot Inc.s Onyx #10, or Calco Chemical Companys F #10.

Our tests have shown that the amount of the carbon powder to be added to the resin varnish is quite critical and should be present within a broadrangeof about 5- to 25% by weight of the total'solids content of the resin varnish, and for best results should beheld within a preferred range of about to ductive; material is employed, the laminate to be electrostatically spray coated, will not be rendered-sufficiently conductive electrically and the conductivity will vary from laminate to laminate within a wide range. On the other hand if too muchof the conductive material is employed, the mechanical properties and appearance of the laminate will be impaired, such as bonding, surface finish, etc.

These; same factors are also affected by-the degree of subdivision and dispersion of the conductive-material in the resin varnish. The carbon powder, should be admixed with the resin varnish in such manner as to render its dispersion as uniform as.p ossil olethus to produce aresultingmixa ture of substantially homogeneous characteristics throughout.

In effecting thisdispersion, a mixing technique should be employed which, on theone hand, sufficiently breaks up andsubdivides large aggregates. or agglomerates of the carbonaceous material, but which, on'theother hand, avoids excessive subdivision andreduction in'particle size, because we have found that both of these extremes result in finished laminates having relatively poor electrical conductivity. bound to any particular theory, we offer the following in explanation of these observed results. If, on-the one hand, the carbonaceous material is dispersed through the resin varnish in the form of relatively: large particles or agglomerates, these particles will be dispersedrelatively far apart in thevarnish and be coated therewith, so

that, upon impregnating the, fibrous sheet base materialv with the varnish, and upon cutting, stacking and hot pressing thersame to form the finished laminate, the carbonparticles will not be. pressed out-into a substantially continuous surface filmof high electrical conductivity but. to thecontrary will tend'to formisolated conduc- If too little of the corn Without being.

tive areas on the surface of the laminate spaced from one another by areas of the pure resin varnish, which will thus tend to electrically insulate the conductive areas from one another, with resulting poor over-all electrical conductivity of the surface as a Whole. On the: otherhand, if the mixing technique is suchasto reducethe carbon particles or agglomerates to an extremely small particle size, they cannot be crushed and spread out to form a substantially continuous and electrically' conductive surface film during the subsequent hot pressing operation in which the laminate is formed, but to the contrary will tend to remain. electrically insulated from one another by interposed resin films with which they are individually coated during the mixing operation. Finally if, the mixing is carried out in such manner as to reduce the carbonaceous material to an intermediate particle size comprising relatively small agglomerates of the ultimate particle size, dispersed relativelyclose together in, the resin varnish, then during the hot pressing operation to-form the finished laminate, these particleswill be crushed and-spread out suificiently to contact one another andthus form a substantially continuous surface filmof the carbonaceousmaterial, thus to provide a surface of high electrical conductivity.

Inconnection with the above, we have found that if the carbonaceous material is admixed with.

the resin varnish by way of a conventional stirring action, such as by the use of a propeller-agitator, the material is dispersed in the form of relatively;

large agglomerates oraggregates, dispersed rela-- tively far apart in the varnish with resulting poorelectrical characteristics of the finished laminates made therefrom, as above noted. On

the other hand,,we-have observed that if the mixing is carried'out by means of a ball-milling. operation, the carbonaceous material is too fine.- 1y groundand subdivided, again with resulting poor electrical characteristics of the finished.

laminates as above noted. We have further foundthat in order to producelaminates-of high elec trical conductivity, the admixing: of the carbonaceous materialwith the resin varnish, is pref erably carried out with a mixer which operates.

on the principle of an hydraulic shearing action,- such as isobtained with a Premier mixer or that put out by Eppenbach, New Yorknnder the trade;

name Homo-Mixer.

We have further found that the specificgravity,

of theresulting varnish having the carbonaceous.

material dispersed therein, is critical in order to provide in the finished laminates, a surface film of high electrical conductivity, and that this specific gravity should lie within the range ,of 1.00 .to.

1.04. and preferably within the range of- 1.00 to 1.02. We interpret this to require that the varnish has characteristics such that the fibroussheetv material, upon impregnation therewith, will act.

as-a filter through which the varnish itself penetrates, while-retaining the carbonaceous material on thesurface-thereof in the form of a-substane tiallycontinuous surface film of high electrical conductivity.

Our investigations indicatethat the use of a carbonaceous material, such as-powdered graphite or preferably carbon black, for the conductivematerial in the resin varnish, isvastly superior to the use of metal powders, such for ex- 5. the resin varnish, whereas the metal powders tend to settle out.

Laminated plastic automotive trim components and particularly refrigerator trim or thermal insulating components, such as breaker strips and frames, door panels, etc., may, and often do, require the same baked-on enamel coating as is applied to the metal portions of the automobile body or refrigerator cabinet. Also such laminated plastic components are usually required to be made up in special shapes involving sectional curvatures or angles or both.

In Patent No. 2,415,763, to the applicant, P. Ryan herein, there is described a so-called fast cycle method of producing resinous laminates of novel construction, which are capable of receiving a baked-on enamel coating without blistering or delaminating, and which can be produced in substantially any shape and sectional configuration from stacked resin varnish impregnated sheets and in a single hot pressing operation involving a pressing time of but a few minutes duration, and which can thereafter immediately be removed from the press while-hot and without injury to the laminate.

As brought out in said patent such laminates are produced by: impregnating fibrous sheet material witha thermosetting synthetic resin varnish to a relatively high resin content, substantially exceeding the weight of the fibrous sheet material therein, and impregnating other fibrous sheet material with a thermosetting resin varnish to a relatively low resin content, substantially less than the weight of the fibrous sheet material therein; forming a stack comprising superimposed layers of the relatively low resin content sheet material, on which is superimposed on side only of the stack, a surface sheet of the relatively high resin content sheet material; subjecting the stacked assembly to combined heat and pressure in a heated press until the resin content thereof is in the transition stage between thermosetting and thermoset conditions; thereupon momentarily relieving the pressure to permit residual gases to escape through the relatively low resin content and hence porous body portion and surface of the assembly; and thereupon resuming the pressure until the resin has been cured to the thermoset condition and the assembly consolidated into a unitary laminate, one surface of which i. e., the I relatively high resin content surface, is relatively hard, smooth and imporous surface and adapted for reception of a baked-on enamel coating, while the remaining body portion and opposite surface of the laminate remains sufficiently porous by reason of the relatively low resin content thereof, to permit the escape of residual gases evolved, without delamination or blistering or marring the high resin content surface, whereby the laminate may be removed from the press while hot and may subsequently receive a bakedon enamel coating without injury.

The present invention is peculiarly adapted to the production of resinous laminates of the character described in said Ryan patent and in which the laminate surface of high resin content which is adapted for reception of the bakedon enamel coating, is also rendered electrically conductive in the manner aforesaid.

By way of specifically illustrating the production of a resin varnish applicable to the production of electrically conductive laminates in accordance with the invention, a resin varnish is made up as follows:

Example I The following materials and quantities thereof are charged into a steam jacketed kettle, equipped with a condenser, agitator and vacuum pump.

Ingredient Quantity Oresylic acid (boiling range l80/230 O.) 603 lbs. Phenol (M. P. 40 C. 263 lbs. Formaldehyde (37% aqueous solution) 890 lbs. Caustic Soda (flakes) 1 lb. 10 oz.

The steam is turned on in the kettle jacket and the batch brought up to boiling (100 C.) in

about 20 to 35 minutes, the batch being thereafter refluxed for about 50 minutes at a steam pressure in the kettle jacket of about pounds per square inch (p. s. i.) and with cooling water circulating through the condenser. After refluxing, the kettle is arranged for vacuum distillation, and distilled under a vacuum of about 20 to 28 inches of mercury, and at a temperature of 54 to 65 C., until 365 pounds of water are removed.

Upon completion of the distillation, the vacuum is broken and 14 pounds of stearic acid added and the batch agitated until the stearic acid is dissolved. Thereupon 50 gallons of 99% isopropyl alcohol are added with agitation and circulation of cold water through the kettle jacket for a period of about 15 to 20 minutes, resulting in a resin varnish having the specifications set forth below as Varnish A.

The resulting Varnish A is admixed in the proportions of 250 pounds of the varnish to 13 gallons of isopropyl alcohol in open drums, and subjected to the action of a mixer operating on the principle of an hydraulic shearing action such as the aforesaid Homo-Mixer, put out by Eppenbach, New York, N. Y., or a Premier mixer, and 1'7 pounds of carbon black added as rapidly as the varnish will allow, and the mixing continued until a smear is obtained which on visual inspection is free from carbon lumps. The varnish is thereupon allowed to age at room temperature for at least four hours before using in order to allow the specific gravity to stabilize. The resulting varnish will then have the specification set forth below as Varnish B. As above stated, a suitable carbon black is Cabot Inc.s Onyx #10 or Calco Chemical Co.s F #10. As above stated the specific gravity of Varnish B is critical and should be held within limits of 1.00 and 1.04 and preferably within 1.00 and 1.02,

and may be adjusted within these limits where necessary by suitable additions of isopropyl alcohol.

Varnish A Varnish B specific gravity 1. 025-1. 035 1. 000-1. 020 viscosity (Centipoise) 20-50 50-70 percent solids (by wt. of total varnish) 42-46 34-38 Set time (seconds at 135 0.). 525-625 650-750 percent carbon black (by wt. of resin solids) 15 For producing resinous laminates which are electrically conductive throughout, av suitable fibrous sheet material, such as kraft paper of about 2 to 10 mils in thickness, usually about 3 to 4 mils, and made preferably from sulfate kraft pulp, is fed progressively from a roll thereof through a bath of Varnish B, the so impregnated paper being fed out of the bath betweensqueeze rolls for removing the excess aeaagwa.

T varnish, the paper beingrfedithence through an oven forv drying the resulting resin varnish impregnated paper. andremovi'ng the volatile. constituents therefrom. Thepressure onthe squeeze rolls is so adjusted that'after oven drying, the

solids content of the resin will constitute about 60% of the paper weight. The paper is thereupon cut into sheets, and the sheets stacked to the depth ofthe desired laminate, and the resulting assembly subjected to' a hot pressing opera.-

electrically, but which is faced with surface sheetsof high electrical conductivity on both the opposite outer surfaces thereof, some of the kraft paper is impregnated in' the manner aforesaid with resin Varnish B', while other of the paper is impregnated with resin Varnish A above, or more preferably with a resin varnish produced as set forth in said Patent-2,415,763, or" other conventional thermosetting resin varnish containing noconductive material. The paper impregnated withthe conventional phenolic resin varnish, is

cut and stacked in thedesired thickness-to form the body portion of the laminate, while theupper and lower surfacesof this stacked assembly are faced with sheets of the kraft paper impregnated with the resin Varnish B; The stacked assembly isthereupon hot pressed in a hydraulic press in the manner above described, and allowed to cool down under pressure in the press before removing.

For producing a fast cycle" laminate in accordance with a preferred embodiment of our invention, having asingle electrically conduc-- tive surface layer adapted for reception of a baked-on enamel coating, we employ for the main body of the laminate, including one of the exposed surface layers, superimposed layers of a relatively-thick and porous sheet material,

such kraft paper made of a 100% sulfate kraft pulp; of for example of T to 11 mils in thickness, which is impregnated to" a relatively low resin content with a conventional thermosetting' resin varnish as aforesaid, the degree of resin varnish impregnation being such for example as to produce on subsequent oven drying, a final dry resin content equal to about 50 to 85% of the weight of the fibrous sheet material, or equal to about to of the total weight of the so. For the. opposite.

mils in thickness, and which is rather heavily impregnated with the carbon black. containing resin Varnish B,- the impregnation being. carried to such an extent as will result on subsequent oven dryingrin. a solids resin content equal to:

about 120 to 185% of the weight of'the: paper,

or: equatftouabout 55 .110 or the total weight of the so impregnated paper.

Fromthesqueezerolls onthe exit sideofthe resinis varnish bath,.,the: soimpregnated sheet 1 material is fed progressively through an oven wherein; it isisubi'ectedi to a high velocity counterflow aincurrenta maintained at about to 1 50 C... 'Ihe:rate:o.pap er feed is so regulated thatzeach section thereof remains in the oven andli's subiected to the. elevated temperature aforesaid, for-arr interval not only sufiicient to volatize and remove the solvent, but also to cure the resin; to a .state bordering upon the endv of the: B?- stage;. The: curingzof the resin in the sheet materials-ta the' condition: aforesaid can be precisely. controlled; in the: process of ovendrying; since. butta.v single: thickness of the sheet material isibeing acted upomand the rate of feed ofithepapen throughrthe oven can be carefully controlled and; adjusted. For the oven drying, conditions. above stated; the resin will be: curedtoith'e proper: extent; by so regulating the feed.

that each. portion. of. :the'. paper: remains in the oven .for' about.%.minutez to about 4 minutes, and preferably about 1 minute to 2 minutes, it.

bemg-lunderstoodithat the paper enters the: oven atisubstantia'lly room .temperature.

The so treatedpapen is then cut into sheets of' appropriate size toform the laminated structure; and the sheets are. then stacked to the extent required for producing a laminate of the thickness desired; For this purpose, the paper impregnatedtothe lower resin. content with the straight phenolie resin, isv employed for the main body portion; and: one surface: of the laminate,

wh-ilexfor the-opposite surface a sheet of theto-providepressures ofi about-1000 to 3000lpounds per: square inch; at temperatures of about 1 65 to C.,. for purposes of hot pressing the: stack to consolidate thelaminae into. the finished laminate, while imparting: the desired final con-- figuration-thereto; and at the same time cornpletely' converting the resin from the 13" state to: the fully thermosetor '6 state.

Pressure isapp'liedi by depressing the pistonof the: apparatus for only a brief period initially, a matter of: only about 15- to- 20 seconds, whereupon thepiston is-momentarily elevated and thepressure released t'o-permit escape of volatilized material. pressed'a'nd the: pressure applied for the remaining. interval. required to convert the resin from the thermosettingatoa the thermoset condition- For the conditions 0t temperature and pressureabove stated; the 1301;811:110?) pressing interval thus required-willvary from about 1 to '7 minutes, depending onthe-particular temperature and type of resin employed. The higher the temperature the. shorter the interval for. initial pressure release and for total hot pressing time required within the limits above stated. As soon as the hot pressing is completed, the laminate may be.

pregnati'ng the fibrous sheet material with the varnish;- and thereafter oven drying the same.

Figures 2 to' 4' inclusive are perspective views,

partially exploded, showing stacked assemblies Thereuporr the piston is again de-- of resin varnish impregnated sheets for producing laminates in accordance with the various modifications of the invention above described.

Figure 5 is a perspective view of a suitable form of apparatus for eelctrostatically spray coating the electrically conductive laminates of the invention; while Figures 6 and '7 are sectional views taken respectively at 6-6 and 'il of Fig. 5.

Referring to Fig. 1 the fibrous sheet material l, such as sulfate kraft paper, is progressively fed from a roll I I thereof over a guide roll l2 into a bath l3 of resin varnish contained in a tank M, the paper passing within the bath under a guide roll I5 and thence out between the squeeze rolls [6 for squeezing oif the excess varnish, the strip being fed thence through an oven [6a for oven drying the resin varnish impregnated paper to remove volatiles, the strip being then wound up into a roll l1.

Fig. 2 shows a stacked assembly of resin varnish impregnated sheets, the body and lower surface laminae of which are impregnated with a conventional phenol-formaldehyde resin varnish while the upper lamina 2| is impregnated with a resin varnish having dispersed therein an electrically conducting material in a fine state of subdivision, such as carbon black.

In Fig. 3 the laminae comprising the body portion, 22 of the stacked assembly are impregnated with a conventional phenolic resin varnish, while the upper and lower surface sheets 23 and 24 are impregnated with the varnish incorporating the electrically conductive material such as carbon black. In Fig. 4 the individual sheets of the entire assembly 25, including the upper and lower surface sheets, are impregnated with the resin varnish containing the electrically conductive material.

Referring to Fig. 5 laminates such as 26, 21, produced in accordance with any of the Figs. 2 to 4 modifications, are electrostatically spray coated by suspending the laminates individually on metal hooks as at 28, 29, passing through drilled holes as at of the laminates. The hooks such as 28, 29 are in turn mounted on transverse support as at 3|, which in turn are carried by uprights as at 32, the latter in turn being mounted upon a driven conveyor mechanism 33, longitudinally displaceable in a stationary guide way 34.

Mounted alongside of the guide way 34 is a wire grid or network assembly shown generally at 35, consisting of a substantially rectangular conductive framelike structure 38, between the upper and lower horizontally extending portions of which a series of wires such as 31, extend in horizontally spaced relation to one another, toform a wire grid. The entire assembly 35 is mounted on insulating supports as at 38.

Mounted above the grid structure 35 is a horizontally extending conductor 39, suspended from insulating supports as at 40. A source of high direct current electrical voltage, such as 4| of, for example 220,000 volts, has its negative terminal connected to the grid structure 35 and its positive terminal connected to the overhead conductor 39, over connections 42, 43 as shown. The

metal hooks 30, have secured thereto, metal con-' tact shoes 44, adapted slidably to engage the overhead conductor 39, as the conveyor mechanism 33 moves along the guide way 34. Mounted adjacent one end of the grid 35 are a series of spray guns, as at 46, arranged to spray paint or other suitable coating material into the space between the laminates 26, 21 and the grid structure 35,

10 and in a direction substantially parallel to the direction of travel of the laminates. I

Thus as each laminate, such as 41, is propelled opposite the grid structure 35, the voltage 4| is impressed between the grid structure 35 and the laminate, by virtue of the electrical connections above described, and in such polarity that the grid structure 35 is negative relative to the laminate. Accordingly as the paint or other coating material, is sprayed by the guns 4-6 in the form of a suspended mist or cloud, as at 50, between the grid and the laminate, the suspended particles of the coating material, assume a negative charge and are thus drawn to and deposited uniformly upon the exposed surface 5| of the laminate to be coated in the manner illustrated in Fig. '7. As soon, however, as each laminate passes beyond the grid 35, the voltage 4| is disconnected therefrom, by reason of the disengagement of the associated contact shoe 44 from the overhead conductor 39.

By way of illustrating the effectivenes of the carbon black in the resin varnish, in imparting electrical conductivity to the laminates, a series of electrical measurements were made on laminates made from a conventional phenolic resin varnish, and other laminates made from the carbon black containing varnish of the present invention, these lamintates having overall dimensions of about 30 x 45 in. and being of equal thickness, approximately .075 in. The resistances of the laminates as measured in the 45 in. dimension, which were made from the conventional phenolic resin varnish, were found to be well over one hundred billion ohms, as compared to resistances of under ten thousand ohms and under for laminates in accordance. with the present invention incorporating carbon black in the varnish. Resistances of this low order were found to be entirely suitable for electrostatic spray coating, whereas the laminates made of the straight phenolic resin varnish could not effectively be so coated.

What is claimed is:

l. A hard, rigid and non-deformable resinous laminate, capable of withstanding temperatures in excess of 300 F. and of receiving a baked-on enamel coating without blistering or delaminating, said laminate comprising the heat and pressure reaction product of a multiplicity of superimposed and thermosetting resin-impregnated sheets of fibrous material, said resin being reacted to the thermoset condition in said laminate and integrally uniting said sheets of fibrous material therein, one surface sheet of said laminate being high in resin content comprising about to by weight of said sheet material and providing a smooth, hard and imporous exposed surface adapted for reception of said baked-on enamel coating, the remainder of said laminate, including the body and opposite surface sheet thereof, being low in resin content comprising about 50 to 85% by weight of saidsheet material and sufficiently porous to permit the escape therethrough of gases evolved on heating, the resin content of said surface sheet high in resin content having uniformly dispersed therein about 5 to 25 by weight of said resin of an electrically conductive carbonaceous material in a fine state of subdivision, and in amount such as to render said surface sufficiently conductive to the flow of direct current as to permit of electrostatically spray coating said surface with enamel and the resin content of said remainder of said laminate ill being substantially tree of said conductive material.

A hard, rigid 'and'rnon-deformable resinous laminate, capable of withstanding temperatures in excess of2300 and of .receiving a baked-on enamel coating without'blistering or delaminat- :-ing,.said laminate comprising the heat and pres- :sure :reaction :product of :amultiplicity .of superimposed and thermosetting resin-impregnated sheetsof fibrous material,1said:resimbeing reacted :to the thermoset'conditionqinzsaid laminate and J integrally zuniting said sheets .of fibrous material therein, one surface-sheet of :said laminate :being "high in resin :content comprising about 120to 185% :by weight of said sheet material "and :proriding. a smooth, hard and Limporous exposed surface adapted for reception of said baked-on -enamel coating, the remainder=of said laminate,

said surface sufficiently conductive to -the:;flow --of direct current as :to :permit of electrostatically spray coating said surface with-enamel and the resin content of said remainder of said laminate being substantially free of said conductive material.

3. A hard, rigid and nonsdeformable resinous laminate, capable of withstanding temperatures in excess of 300 'F. and of receivinga "baked-on enamel coating without blistering or delaminating, said laminate comprising'the'heat and'pressure reaction product of a multiplicity-of superimposed and thermosetting resin-impregnated sheets of fibrous material, said-resin being reacted to the thermoset condition in'saidxlaminate and integrally uniting said sheets of fibrous material therein, one surface sheet ofsaid laminate bein high in resin content comprising about ,120 to 185% by weight of said sheet material and providing a-smooth, hard and imporous exposed surface adapted for reception of said baked-on enamel coating, the remainder of said laminate, including the body and opposite surface sheet thereof, being low in resin content comprising about 50 to 85% by weightof-saidsheet material and sufiiciently porous to permit the escape therethrough of gases evolved -on heating, the

resin content of 'said'surface sheet high in'resin content having uniformly-dispersed therein in a fine state of subdivision, about to:% of carbon powder by weight of said resin,thereby to render said surface suihciently conductive'to the flow of direct current as to permit of electrostatically spray coating saidsurface with said enamel and the resin content of said remainder of said laminate being substantially free of said conductive material.

'4. A hard, rigid and non-deformable resinous "185% by weight .of said sheet 'material :and proriding a smooth,' hardand imporousiexposedtsur- "face adapted for reception :of said abaked-on enamel coating, the remainder .-of said laminate including 'the'body and opposite surface sheet 'ithereof, being 'low in resinacontent comprising :about 50 to .by weight iof'said :sheet material and sufficiently porous to permit the escape therethrough of gases evolved .on heating, the resinacon'tent of said surface sheet high in-resin -oontentifliaving .uniformly :dispersed therein in a fine stateiof subdivision, about '10 to15% of .car- --bon :black by weight of said resin, thereby to render said surface sufficiently iconductive to the flow of direct current as :to permit .of electrostatically spray :coating said surface with said enamel and the resin content of said remainder of said laminate being substantially free of .said .rconductive material.

5. A resinous "laminate comprising surface :sheets of'fibrous material superimposed on inter- -:-mediate sheets .of fibrous material, .said sheets tbeingimpregnated with and consolidated into :a

' unitarystructure bya thermoset synthetic resin,

the resin content .of :at Eleast ,one said :surface zshee't o'fssaid'laminatejhavinguniformly-dispersed therein about 5 :to 25% by :weight of saidresin of an electrically conductive carbonaceous material in-aifine state :of subdivision, said material being .present in amount-sufiicient Ito render sa'id surface electrically :conductive to direct :current flDWiZJld-SUOII as toadapt saidsurface to electroistatic :spray .painting,'the :resin content of said intermediate sheets being substantially free from :said electricallyconductive material, anda coating of electrostatically andspray-a-ppliedpaintwan .saidone surface sheet.

iltefercnces Cited in the rfile of this patent UNITED STATES PATENTS Number Name Date 951,605 Baekeland Nov. 30, .1909 $564,775 Frederick Dec. 8, 1925 1,953,111 Home Apr. 3, 1934 1,975,918 Bradley Oct. 16, 1934 2,112,762 I Chatfield :Mar. .29, 1938 2,343,740 Birmingham Mar. 7,1944 2,359,097 ,Elsey. Sept. 26, 1944 2,397,082 Barker Mar. 26, 1946 2,415,763 Ryan Feb. 1 -1 ,;194.7 2,427,700 Atkinson. et-al. .Sept.,23, .1947 12,440,300 Rushmer etral Apr.,.27,.l948 12,498,493 HickerneH Feb. 21, 1950 "2510;727 ,Sussenbach June 6, 1950 

1. A HARD, RIGID AND NON-DEFORMABLE RESINOUS LAMINATE, CAPABLE OF WITHSTANDING TEMPERATURE IN EXCESS OF 300* F. AND OF RECEIVING A BAKED-ON ENAMEL COATING WITHOUT BLISTERING OR DELAMINATING, SAID LAMINATE COMPRISING THE HEAT AND PRESSURE REACTION PRODUCT OF A MULTIPLICITY OF SUPERIMPOSED AND THERMOSETTING RESIN-IMPREGNATED SHEETS OF FIBROUS MATERIAL, SAID RESIN BEING REACTED TO THE THERMOSET CONDITION IN SAID LAMINATE AND INTEGRALLY UNITING SAID SHEETS OF FIBROUS MATERIAL THEREIN, ONE SURFACE SHEET OF SAID LAMINATE BEING HIGH IN RESIN CONTENT COMPRISING ABOUT 120 TO 185% BY WEIGHT OF SAID SHEET MATERIAL AND PROVIDING A SMOOTH, HARD AND IMPOROUS EXPOSED SURFACE ADAPTED FOR RECEPTION OF SAID BAKED-ON ENAMEL COATING, THE REMAINDER OF SAID LAMINATE, INCLUDING THE BODY AND OPPOSITE SURFACE SHEET THEREOF, BEING LOW IN RESIN CONTENT COMPRISING ABOUT 50 TO 85% BY WEIGHT OF SAID SHEET MATERIAL AND SUFFICIENTLY POROUS TO PERMIT THE ESCAPE THERETHROUGH OF GASES EVOLVED ON HEATING, THE RESIN CONTENT OF SAID SURFACE SHEET HIGH IN RESIN CONTENT HAVING UNIFORMLY DISPERSED THEREIN ABOUT SPRAY COATING SAID SURFACE WITH ENAMEL AND THE CONDUCTIVE CARBONACEOUS MATERIAL IN A FINE STATE OF SUBDIVISION, AND IN AMOUNT SUCH AS TO RENDER SAID SURFACE SUFFICIENTLY CONDUTIVE TO THE FLOW OF DIRECT CURRENT AS TO PERMIT OF ELECTROSTATICALLY SPRAY COATING SAID SURFACE WITH ENAMEL AND THE RESIN CONTENT OF SAID REMAINDER OF SAID LAMINATE BEING SUBSTANTIALLY FREE OF SAID CONDUCTIVE MATERIAL. 